Poizner, to separate himself from Whitman, made immigration the defining issue of his campaign. He expressed strong support for the controversial Arizona immigration law and attacked Whitman for opposing it.

Poizner criticized the decision by the City of Los Angeles to boycott Arizona businesses to protest the immigration law. He pledged to require all state contractors to provide proof of their employee's immigration status, boycotting any firms that have hired illegal immigrants.

Whitman, who consistently led Poizner in the polls, sought to show that while she opposed the Arizona law, she was not weak on illegal immigration. In her own television advertising, she promised "to secure our border with absolutely no amnesty," as part of her effort to "save California."

The immigration debate could compromise Republicans' chances of winning in November. Hispanics comprise approximately 37 percent of California's population and candidates cannot afford to alienate Latino voters, a large majority of whom oppose the Arizona law and favor earned legalization.

In the fall, Whitman will face Democrat Jerry Brown, the state's Attorney General, who served as governor from 1975 to 1983.

Funding could be a challenge for Brown. The GOP primary has seen massive levels of spending, with Whitman spending over $60 million of her own money and $80 million overall, and pledging to spend up to $150 million of her own money in the general election.

Electability Key Factor in Senate Race

Fiorina received an unexpected boost from the endorsement of former Alaska governor Sarah Palin, even though DeVore was supported by Tea Party groups.

Palin recorded a telephone message for Fiorina, urging voters to "help get our country back on track" by voting for the former executive.

Fiorina spent a lot of her own personal wealth on the campaign, a point likely to be seized upon by Democrats in the midterm elections. Campbell struggled to keep pace, temporarily withdrawing television advertising last week. A libertarian on most social issues, Campbell focused his rhetoric on his electability in the final days of the campaign.

In November, Fiorina is likely to face a heated battle with Boxer, who has been in the Senate for 17 years.